In recent years, offshore wind power system has attracted interest as an effectively way of using natural energy for the prevention of global warming. Wind power generation requires a power converter for converting the wind turbine rotation into power, and a control unit for controlling the power conversion. The power converter usually utilizes switching of high efficiency power semiconductors, and the semiconductor elements are insulated and protected by being sealed with a gel or a resin.
The offshore atmosphere is more humid and saline than the onshore environment, and therefore there is a need to be more moisture-resistant power converters and control units in order to use in the offshore wind power systems.
Another area of interest for the prevention of global warming is automobiles, where low fuel consumption cares are required. In these years, motor-driven electric cars and motor-engine hybrid cars have been getting a lot of attention. The high power onboard motors for driving automobiles are difficult to be driven and controlled with the DC voltage of the onboard battery, and requires a power converter that utilizes switching of power semiconductors for the AC control of the boosted voltage. A power converter that uses switching of high efficiency power semiconductors has become mainstream, and semiconductor elements in such power converters are sealed with a resin for insulation and protection, and, at the same time, miniaturization.
Power semiconductor elements generate heat due to conducting electricity. Cooling structures play an important role in this type of semiconductor elements, and water cooling has become a mainstream method of the cooling. Then, such a power semiconductor element is required to have a waterproofing structure.
A mold-sealed semiconductor device of a structure with excellent moisture resistance is known in which semiconductor elements are mounted on a lead frame, and in which a room-temperature glass coating (heat-less glass coating) is used to mold and seal the semiconductor elements, the bonding wires and the bonding area after wire bonding the semiconductor elements to external connection terminals (see, for example, Patent Literature 1).